Ryan Tannehill couldn’t have drawn a much tougher assignment for his NFL debut – on the road, in a loud dome while facing last year’s No. 2-ranked defense. The Dolphins need to keep him upright to have a chance, and the right side of the line is new and untested, with rookie RT Jonathan Martin and …

Things we learned from Tuesday night’s episode of HBO’s all-access show Hard Knocks, the fourth of five in the series:

* CB Vontae Davis never improved his consistency or professionalism, leading to a trade. Defensive backs coach Lou Anarumo, when talking about Davis’ pass interference play in last week’s preseason game against Atlanta, said, “I’ve never seen anything like it. Just a total lack of awareness.” When told by Jeff Ireland …

It made for an interesting contrast when tight end Vernon Davis of the San Francisco 49ers came to South Florida for the 2010 Pro Bowl a couple of years back. Davis, of course, is the big brother – in more ways than one – of Vontae Davis, the Dolphins’ first-round pick in 2009 who this week was shipped off to Indianapolis for second- and sixth-round picks in next year’s draft.

Dolphins fourth-year receiver Julius Pruitt was one of the Dolphins’ best special teams players last year in the nine games he played after being promoted from the practice squad.

But his special teams prowess, nor his receiving skills, were enough to land him a roster spot this season. According to a league source, the Dolphins waived Pruitt today to get the roster down to 75 players by the 4 p.m. deadline. …